Safety conductor



May E9, 1936. E. 0. SCHWEITZER MLWB SAFETY CONDUCTOR Filed March 28, 1952 Patented May 19, 1936 UNITED STATES PATENT OFFICE Application March 28,

18 Claims.

The present invention relates generally to electric conductors, and more particularly to flexible connecting cords such as are generally employed with electric appliances and the like.

Flexible cords for providing an electrical connection to appliances and other portable electric devices have always presented a considerable hazard. Electric cords used in such service are often subjected to severe wear and tear and even to mechanical injury of such nature that dangerous faults frequently develop in the insulation as Well as in the conductors themselves, and faults of this nature invariably breed trouble.

Thus, a partially broken conductor will present a relatively high resistance to the flow of current at the break and may be heated to a dangerously high temperature. Faults in the insulation permit short circuits and attendant arcs between the conductors and also between the conductors and surrounding metal objects which are grounded or otherwise connected to the system. The fuse in the main circuit does not afford protection against the dangers resulting from most of the usual types of cord faults since, in view of other devices that are to be supplied with current over the same circuit, the fuse is made of a larger current capacity than that generally taken by the faulty cord.

While my present invention is especially directed to electric cords and similar flexible conductors, it will be readily appreciated by those skilled in the art that the same is applicable to electric conductors in general.

It is a primary object of my present invention to provide means for minimizing the hazards in cident to the occurrence of faults in electric connecting cords due to the rough usage to which they are subjected.

It is another primary object of my present invention to provide means for automatically healing injuries which an electric conductor may sustain.

I provide a cord having at least one fusible conductor. In one preferred embodiment of my invention the cord has a copper conductor and a fusible conductor twisted together so that any strain falling on the cord will be supported by the relatively strong copper conductor. It is obvious that the conductors may extend parallel toeach other within the cord, if so desired. The copper conductor may be stranded and, if desired, may include a few strands of the fusible metal to provide for healing of the copper conductor, and also to provide for more convenient 1932, Serial No. 601,488

and permanent attachment to binding screws or other terminals.

I also contemplate the provision in an electric conductor of an arc extinguishing medium for snufling out any arcs which may be formed and for overcoming or healing injuries sustained by the insulation. This are extinguishing medium may be coated on the metal of the conductor itself or it may be impregnated in, or deposited between successive layers of the insulation surrounding the same. The are extinguishing substance, whether it be employed in connection with my fusible conductor or not, provides a considerable protection against the formation of destructive arcs, which protection is applicable to any conductors which are closely grouped as, for example, conductors in a conduit or on a control panel.

This are extinguishing medium may be any known arc resisting substance having suitable dielectric and physical characteristics. I have found'that chlorinated naphthalene is admirably suited to the purpose. Asphaltum may be used also or instead. In addition toits arc quenching and healing properties, chlorinated napthalene when heated, also gives off a gas having a characteristic odor. This gas and odor may serve as a warning of impending trouble or as an aid in the location of the fault.

In order to acquaint those skilled in the art with the teachings and practice of my invention I shall now describe several specific embodiments of the same, reference being had to the accompanying drawing, in which:

Figures 1, 2 and 3 illustrate electric conductor cords embodying the principles of my present invention;

Figure 4 is an enlarged sectional View taken along the line 4-4 of Figure 1; and

Figure 5 is an enlarged sectional View taken along the line 55 of Figure 2.

Figure 1 of the drawing illustrates a connecting cord of the type commonly known as twisted pair, which consists of two conductors l l and I2 which are separately insulated and twisted together. Referring to both Figures 1 and 4, the conductor 1 l comprises a single solid conductor of a suitable fusible metal. Any low melting point metal may be used such, for instance, as a lead alloy; a tinlead alloy; a lead-antimony alloy; an alloy of lead, tin and antimony; zinc; or a zinc alloy; or any other suitable fusible metal. The fusible conductor may be a single solid conductor or, where a greater flexibility is desired, may comprise a number of stranded conductors. The conductor H is coated with a layer It of an arc extinguishing substance, and surrounding this is a sheath M of rubber insulation or the like. An outside covering of braided fabric !5 is provided to protect the rubber insulation and to enhance the ap pearance of the completed cord.

The conduct 1' l2 comprises a plurality of strands of copper or bronze or other conducting material having a relatively high tensile strength. It may or may not include a few strands of fusible metal. The conductor i2 like the conductor l l is provided with a coating of arc extinguishing material i3, a sheath of rubber insulation l4 and an outer covering of braid Hi. In this construction the copper conductor 2 is depended upon to support any mechanical strains to which the cord may be subjecter. The fusible conductor i I may of course be stranded.

In Figure 2 I have illustrated a connecting cord comprising a pair of stranded, fusible metal conductors 2|, each of which is separately encased in a sheath 2? of rubber or similar insulating material. The two conducto 2!, together with a strand 23 of fibrous material, are twisted together and surrounded with a heavy rubber outer tubing 24. The strand 23 may be included merely as a filler to make the twisted assembly present a more nejzrly round contour to the rubber casing 24, or it may be employed to relieve the soft metal conductors 2| of mechanical strains. The rubber casing 24 also lends strength to the completed device. The voids within the casing 24 are filled with a body of the arc extinguishing substance 25.

Figure 3 illustrates a connecting cord compris ing a pair of conductor strands 31 each of which is m'zcle up of a large number of strands of fusible metal. The conductors 3i are separately coated with an arc extinguishing substance and enclosed in soft rubber sheaths They are then twisted toget ier and enclosed in a supporting sleeve or tubing 34- which lends strength rigidity to the finished cord. The assembly is then covered with a protecting braid The tubing 34 may conveniently be made of shellac cellulose, regenerated cellulose, common y known by the trade name Cellophane, or similar material which can be formed over the twisted conductors.

In operation, my improved conductor acts to heal any slight injuries which it may sustain, and in the event that any injury may be too severe to permit healing of the same, the conductor removes itself from service with a minimum of hazard to its connected equipment or to nearby objects such as adjacent conductors, and inflammable material.

Should the cord be kinked or bruised so that its conductor becomes partially broken, the heat produced by current traversing the rupture will melt the same to permit the broken portion to fuse together, and to t reby repair the damage. However, if the run to the conductor is of sure such a nature that a proper healing of the same is impossibl the melted conductor will separate to completely open circu and the arc extingi lshing medium surrounding L38 conductor will aid in extinguishing the resultant arc. A conduc or of copper or a similar metal can lot heal in this ner. Thor vcntion in v ductor, I prefer a few strands of in ed at low temperature to epair injuries to the conductor in the above describe-c. manner.

When a break occurs in the insulation, permitstrands ting the metal conductors to come into contact with each other, a short circuit current will flow between them. The heat of the short circuit current will melt the contacting surfaces of the fusible conductors, causing those surfaces to recede from each other, whereupon an arc will be drawn between them The heat of this are will cause the arc extinguishing compound, which surrounds the separate conductors, to flow into the space between them so to extinguish the arc and repair the insulation.

However, if it should be impossible for the conductors to separate in the manner described, the fusible conductor will melt in two, thereby functioning as a fuse to interrupt the short circuit current. Such an emergency may arise when the damaged cord becomes pinched so as to hold the bared conductors together. The fusible conductor in melting to interrupt the circuit will necessarily draw an are which will be quickly extinguished by the action of the arc quenching compound surrounding the conductor.

In opening the circuit in response to a short between the metal conductors, my improved cord responds much more quickly than does a conventional fuse. The conventional fuse is heated only by current traversing the fixed resistance of the fuse while in my device the much greater heat generated in the fault itself is also available for melting the conductor to sever it.

While I have shown and described a number of specific embodiments of my invention, it will be apparent to those skilled in the art that the principies thereof are capabl of a much broader application. I therefore do not intend to be limited by the specific disclosure but wish to be limited only by the scope of the appended claims.

1' claim:

1. In combination in a device of the class described, a pair of separately insulated electric conductors at least one of which is composed of a fusible metal, and an arc extinguishing substance associated with said conductors, whereby in the event of a contact between said conductors and a flow of current between them the L fusible conductor will melt to cause its surface to recede to separate the conductors and the arc extinguishing substance. will quench the resulting are.

2. A flexible cord including a conductor and 3 insulation surrounding the conductor, the com ductor being of fusible metal which will fuse to reestablish the continuity of the low resistance of the conductor in the event of the formation of a high resistance fault therein, and an are extinguishing medium interposed between said insulation and said conductor for quenching arcs resulting from melting and separation of said conductor by reason of a fault occurring therein of sufiicient intensity to prevent reestablishment of the continuity of the low resistance of the conductor.

3. A low voltage flexible insulated conductor comprising stranded wires some of which are of high tensile strength and at least one of which is of low tensile strength and fusible, said wires being in conductive relation throughout their length whereby, upon the occurrence of a high resistance fault in the conductor, the fusible wire will fuse to reduce the resistance of the fault, while maintaining the insulated condition of the conductor.

4. A low voltage flexible insulated cord for establishing electrical connections, said cord iii) comprising at least two side by side conductors insulated from one another and enclosed in a flexible casing and, when carrying current, at a voltage difference equal to the line voltage, and adapted to be flexed while in normal use, at least one of said conductors including a low tensile strength fusible wire throughout its entire length adapted to interrupt the circuit of the cord upon overheating of any part thereof, at least one of the two insulated conductors comprising a stranded wire to facilitate flexing of the cord.

5. A conductor for extending an electric circuit from an electric supply line to an electrically operated device comprising a flexible. relatively long conductor formed of a fusible metal, an arc extinguishing material in heat absorbing proximity to said conductor throughout its length, and an enclosing insulating cover for said arc extinguishing material extending the full length of said conductor.

6. Means for extending a circuit to an electrically operated device comprising a plurality of conductors, one of said conductors comprising a flexible stranded copper conductor, another of said conductors comprising a fusible metal, are extinguishing means extending about and completely enclosing the surface of each of said conductors, and insulating material separately enclosing said conductors and formed about said arc extinguishing means.

'7. Means for extending a circuit to an electrically operated device comprising a plurality of conductors, one of said conductors comprising a flexible stranded copper conductor, another of said conductors comprising a fusible metal, are extinguishing means disposed in heat absorbing proximity to one of said conductors throughout its length, and insulating material separately enclosing said conductors and formed about said arc extinguishing means.

8. A self-sealing and self-protecting conductor of a length substantially exceeding one foot comprising a flexible current bearing member formed of a fusible metal interwoven with a stranded copper conductor, arc extinguishing material enclosing said conductor, and an enclosing insulating casing extending the entire length of the conductor.

9. A flexible cord for extending an electrical circuit to an electrically operated appliance comprising a pair of conductors extending side by side, one of said conductors being formed of a fusible metal, arc extinguishing material enclosing each of said conductors, a separate insulating cover for each of said conductors formed over said are extinguishing material, and an outer enclosing insulating cover over said separate insulating covers.

10. A conductor comprising a fusible current carrying member of low tensile strength enclosed within an arc extinguishing medium, said member fusing upon development of a fault within the length of the conductor to prevent objectionable increase in resistance in said conductor, and an insulating flexible cover enclosing said medium, said medium providing for quenching of any arcs occurring due to separation of said conductor by the melting and receding of the portions of said conductor adjacent a fault developing within the length of the conductor which cannot be overcome by the aforementioned fusing of said member.

11. A conductor comprising a fusible current carrying member of low tensile strength having an arc extinguishing medium in heat absorbing proximity thereto throughout its length, said member being composed of a material proportioned to fuse upon the development of a fault Within the length of the conductor to prevent obiectionable increase in resistance in said conductor otherwise resulting from said fault, and

an insulating flexible cover enclosing said member and said are extinguishing medium, said medium providing for quenching of any arcs occurring due to separation of said conductor by the melting and receding of the portions of said conductor adjacent a fault developing within the length of the conductor which cannot be overcome by the aforementioned fusing of said member.

12. A flexible cord for extending an electrical circuit to an electrically operated appliance comprising a pair of stranded conductors, one of said conductors having a fusible metal interwoven therein, a coating of chlorinated naphthalene enclosing each of said conductors, a separate insulating cover for each of said conductors formed over said coatings, and an outer enclosing insulating cover over said separate insulating covers.

13. A flexible cord for conducting electricity from a point of supply to a point of use comprising a plurality of conductors, each of said conductors being individually insulated, and an arc suppressing material impregnated within the insulation of each conductor, said material being of a character to be fused by heat incident to arcing between two of the conductors, due to breakdown of the insulation thereof, and acting to extinguish the arc and to flow between the conductors in the zone of said breakdown and there form an insulating barrier between said conductors effective to prevent further arcing therebetween.

14. A conductor for extending an electrical circuit from an electric supply line to an electrically operated device comprising a flexible relatively long conductor having a fusible metal therein, and an enclosing insulating cover extending the full length of said conductor and including chlorinated naphthalene in contact with said conductor.

15. A flexible cord for extending an electrical circuit to an electrically operated appliance comprising a pair of conductors, a coating of chlorinated naphthalene enclosing each of said conductors, a separate insulating cover for each of said conductors extending substantially the full length of said conductors about said coatings, and an outer enclosing insulating cover over both said separate covers, said coating being fused by heat incident to arcing between said conductors, due to breakdown of the coverings thereof, and said outer covering acting to confine the flow of the fused material of said coating and to direct the fused material between the conductors in the zone of said breakdown, the fused material being effective to extinguish the arc and to form an insulating barrier between said conductors effective to prevent further arcing therebetween.

16. As a new article of manufacture, a conductor cord for connecting an electrical appliance to a source of electricity, said cord comprising two conductors insulated from each other and coextensive as to length, each conductor being intended for connection at one end to an electrical appliance and at its other end to a source of electricity, the conductive capacityof each conductor being sufficient to accommodate the normal flow of current to the associated appliance, one of said conductors constituting a fuse and being fusible by flow therethrough of current objectionably in excess of the normal current flow, while said conductors remain insulated from each other.

17. As a new article of manufacture, a conductor cord for connecting an electrical appliance to a source of electricity, said cord comprising two conductors insulated from each other and coextensive as to length, each conductor being intended for connection at one end to an electrical appliance and at its other end to a source of electricity, the conductive capacity of each conductor being sufiicient to accommodate the normal flow of current to the associated appliance, one of said conductors constituting a fuse and being fusible by flow therethrough of current objectionally in excess of the normal current flow, while said conductors remain insulated from each other, the other conductor having a conductivity capacity materially greater than that of said one conductor.

18. As a new article of manufacture, a conductor cord for connecting an electrical appliance to a source of electricity, said cord comprising two flexible conductors insulated from each other and coextensive as to length, each conductor being intended for connection at one end to an electrical appliance and at its other end to a source of electricity, one of said conductors being relatively strong mechanically and the other of said conductors being relatively weak mechanically, said conductors being twisted to gether and the weak conductor being supported and reinforced by the strong conductor, the conductive capacity of said weak conductor being sufiicient to accommodate the normal flow of current to the associated appliance, said weak conductor constituting a fuse and being fusible by flow therethrough of current objectionally in excess of the normal current flow, while said conductors remain insulated from each other, the conductive capacity of said strong conductor being materially greater than that of said weak conductor.

EDMUND O. SCHWEITZER. 

